1. Field of Invention
The present invention is directed to control systems and, more particularly, to process control systems and software therefor that may be used to control and monitor the operation of an industrial facility.
2. Discussion of Related Art
Process control systems are used in industrial facilities (such as manufacturing and power plants) to control and monitor the operation of various pieces of equipment. Examples of such process control systems are described in co-pending U.S. patent application Ser. No. 08/623,742 and U.S. Pat. No. 5,179,710, which are assigned to the assignee of the present invention, and which are incorporated herein by reference.
One use of a process control system is to control the operation of several pieces of equipment in order to execute a recipe. A recipe may be, for example, a procedure pursuant to which a series of steps (e.g., mixing, heating or cooling) are performed on one or more pieces of equipment to yield a so-called "batch" of a product.
Generally, several different pieces of equipment or "units" (e.g., mixers, reactors or packagers), some of which may be physically connected together (e.g., using pipes and valves) to pass ingredients from one to another, are required to produce a batch. When a batch of a recipe is scheduled, it is therefore necessary to specify which procedures are to be performed on which units.
Each procedure executed on a unit is called a "unit procedure." Generally, each unit procedure includes several so-called "operations" to be performed on the unit, and each operation includes several so-called "recipe phases." Each recipe phase is used to control a particular minor processing task of a piece of equipment, e.g., heat or cool, which commonly are referred to as "equipment phases." Control of these equipment phases may be accomplished, for example, with a programmable logic device (PLD).
Using existing systems, when a batch of a recipe is scheduled to be executed on several individual units, a system operator may be required to specify which unit procedures will be executed on which units. To accomplish this task, the system operator may be presented with a so-called "area model," which identifies the units that are available for use, and a so-called "recipe model," which identifies the unit procedures that must be executed to process a recipe. Examples of these models are shown in FIGS. 1 and 2, respectively.
FIG. 1 shows an exemplary prior art area model 100, which includes three classes of equipment: (1) a mixer class, including mixers 102a-102c; (2) a reactor class, including reactors 104a-104c; and a packager class, including packagers 106a-106c. Each piece of equipment in a particular class is capable of performing identical procedures and associated equipment phases.
FIG. 2 shows an exemplary prior art recipe model 200 listing unit procedures that may be executed on a group of units, e.g., the units in area model 100 (FIG. 1), in order to process a recipe. Recipe model 200 is in the form of a sequential function chart (SFC), which specifies the unit procedures that must be executed on appropriate units in order to generate a batch of a recipe.
In an SFC, unit procedures that are arranged horizontally adjacent one another on the same vertical level are executed in parallel, i.e., concurrently, and the various vertical levels of unit procedures are executed sequentially from the top level to the bottom level. The primary function of an SFC therefore is to specify the order in which groups of parallel-executed unit procedures are to be executed, regardless of the equipment on which they are executed, to generate a recipe. Additional information regarding SFCs in general is available from the International Electrotechnical Commission (IEC) in a document entitled Draft IEC 1131-1: Programmable Controllers-Part 3, submitted Feb. 14, 1992, which is incorporated herein by reference.
As shown, recipe model 200 includes five distinct unit procedures 202a, 202b, 204a, 204b and 206. Because the five unit procedures are vertically stacked in the SFC, they are to be executed in sequence from top (i.e., unit procedure 202a) to bottom (i.e., unit procedure 206).
Using only the information in area model 100 and recipe model 200, in addition to the operator's personal knowledge, the operator must specify: (a) which of mixers 102a-102c will execute each of "mix" unit procedures 202a and 202b, (b) which of reactors 104a-104c will execute each of "react" unit procedures 204a and 204b, and (c) which of packagers 106a and 106b will execute "packaging" unit procedure 206.
Because of the limited information in prior art area and recipe models, the equipment operator may assign unavailable or non-functional equipment to perform unit operations, or may fail to assign physically-connected pieces of equipment to perform unit procedures when such connections are necessary. These mistakes can cause malfunctions to occur within the processing facility.